Method of forming CMOS integrated circuitry having halo regions

ABSTRACT

A method of forming CMOS integrated circuitry includes, a) providing a series of gate lines over a semiconductor substrate, a first gate line being positioned relative to an area of the substrate for formation of an NMOS transistor, a second gate line being positioned relative to an area of the substrate for formation of a PMOS transistor; b) masking the second gate line and the PMOS substrate area while conducting a p-type halo ion implant into the NMOS substrate area adjacent the first gate line, the p-type halo ion implant being conducted at a first energy level to provide a p-type first impurity concentration at a first depth within the NMOS substrate area; and c) in a common step, blanket ion implanting phosphorus into both the NMOS substrate area and the PMOS substrate area adjacent the first and the second gate lines to form both NMOS LDD regions and PMOS n-type halo regions, respectively, the phosphorus implant being conducted at a second energy level to provide an n-type second impurity concentration at a second depth within both the PMOS substrate area and the NMOS substrate area, the first energy level and the first depth being greater than the second energy level and the second depth, respectively. Methods of forming memory and other CMOS integrated circuitry are also disclosed involving optimization of different NMOS transistors.

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. applicationSer. No. 08/631,249, filed on Apr. 12, 1996, entitled "A Method ofForming CMOS Integrated Circuitry" listing the inventors as Charles H.Dennison and Mark Helm now U.S. Pat. No. 5,683,927, which is acontinuation application of U.S. application Ser. No. 08/503,149, filedon Jul. 17, 1995, entitled "A Method Of Forming CMOS IntegratedCircuitry" listing the inventors as Charles H. Dennison and Mark Helmand which is now U.S. Pat. No. 5,534,449.

TECHNICAL FIELD

This invention relates to methods of forming complementary metal oxidesemiconductor (CMOS) integrated circuitry, and to methods of formingfield effect transistors.

BACKGROUND OF THE INVENTION

An MOS (metal-oxide-semiconductor) structure in semiconductor processingis created by superimposing several layers of conducting, insulating andtransistor forming materials. After a series of processing steps, atypical structure might comprise levels of diffusion, polysilicon andmetal that are separated by insulating layers.

CMOS is so-named because it uses two types of transistors, namely ann-type transistor (NMOS) and a p-type transistor (PMOS). These arefabricated in a semiconductor substrate, typically silicon, by usingeither negatively doped silicon that is rich in electrons or positivelydoped silicon that is rich in holes. Different dopant ions are utilizedfor doping the desired substrate regions with the desired concentrationof produced holes or electrons.

NMOS remained the dominant MOS technology as long as the integrationlevel devices on a chip was sufficiently low. It is comparativelyinexpensive to fabricate, very functionally dense, and faster than PMOS.With the dawning of large scale integration, however, power consumptionin NMOS circuits began to exceed tolerable limits. CMOS represented alower-power technology capable of exploiting large scale integrationfabrication techniques.

CMOS fabrication does however present a number of challenges to thefabricator as compared to using PMOS or NMOS alone. Specifically,typically independent or separate masking steps are utilized for maskingone of the p-type regions while the n-type region is being doped. Also,the n-type regions are separately masked when the p-type regions arebeing doped. Accordingly, typical transistor flows use one mask each toform the n-channel and p-channel transistor source and drain regions.Higher levels of integration result in denser and denser circuits,leading CMOS fabrication to more difficulties.

It would be desirable to develop methods which further facilitateformation of complementary source and drain regions within asemiconductor substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment at one processing step in accordance with the invention.

FIG. 2 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 3.

FIG. 5 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with one aspect of the invention, a method of forming CMOSmemory integrated circuitry comprises the following steps:

providing a series of gate lines over a semiconductor substrate, thegate lines comprising memory array gate lines and peripheral circuitrygate lines, a first gate line being positioned relative to a firstperipheral area of the substrate for formation of a peripheral NMOStransistor, a second gate line being positioned relative to a secondperipheral area of the substrate for formation of a peripheral PMOStransistor, a third gate line being positioned relative to a memoryarray area of the substrate for formation of a memory array NMOStransistor;

masking the second gate line, the second peripheral PMOS substrate area,the third gate line and the memory array NMOS substrate area whileconducting a p-type halo ion implant into the first peripheral NMOSsubstrate area adjacent the first gate line, the p-type halo ion implantbeing conducted at a first energy level to provide a p-type firstimpurity concentration at a first depth within the first peripheral NMOSsubstrate area; and

in a common step, blanket ion implanting phosphorus into the firstperipheral NMOS substrate area, the second peripheral PMOS substratearea and the memory array NMOS substrate area adjacent the first, thesecond and the third gate lines to form peripheral NMOS transistor LDDregions, peripheral PMOS transistor n-type halo regions and memory arrayNMOS transistor source/drain diffusion regions, respectively, thephosphorus implant being conducted at a second energy level to providean n-type second impurity concentration at a second depth within thefirst, the second and the memory array substrate areas, the first energylevel and the first depth being greater than the second energy level andthe second depth, respectively.

In accordance with another aspect of the invention, a method of formingCMOS integrated circuitry comprises the following steps:

providing a series of gate lines over a semiconductor substrate, a firstgate line being positioned relative to an area of the substrate forformation of an NMOS transistor, a second gate line being positionedrelative to an area of the substrate for formation of a PMOS transistor;

masking the second gate line and the PMOS substrate area whileconducting a p-type halo ion implant into the NMOS substrate areaadjacent the first gate line, the p-type halo ion implant beingconducted at a first energy level to provide a p-type first impurityconcentration at a first depth within the NMOS substrate area; and

in a common step, blanket ion implanting phosphorus into both the NMOSsubstrate area and the PMOS substrate area adjacent the first and thesecond gate lines to form both NMOS LDD regions and PMOS n-type haloregions, respectively, the phosphorus implant being conducted at asecond energy level to provide an n-type second impurity concentrationat a second depth within both the PMOS substrate area and the NMOSsubstrate area, the first energy level and the first depth being greaterthan the second energy level and the second depth, respectively.

More particularly, FIG. 1 illustrates portions of a semiconductor waferfragment in process indicated generally with reference numeral 10. Suchcomprises a bulk silicon substrate 12 which is intrinsically p-doped,with a portion 14 thereof being subsequently n- doped to define ann-well. A series of gate lines are provided over semiconductor substrate12. The discussion proceeds with reference to preferred formation ofCMOS memory integrated circuitry, with some of the gate lines comprisingmemory array gate lines and other of the gate lines constitutingperipheral circuitry gate lines.

Specifically, a first gate line 16 is positioned relative to a firstperipheral area 18 of substrate 12 for formation of a peripheral NMOStransistor. A second gate line 20, is positioned relative to a secondperipheral area 22 of substrate 12 and n-well 14 for formation of aperipheral PMOS transistor. A third gate line 24 is positioned relativeto a memory array area 26 for formation of a memory array NMOStransistor. Typical preferred present day cross sectional widths forgates 24, 16 and 20 are 0.40 micron, 0.42 micron, and 0.55 micron,respectively. In otherwords, the desired relationships are that thecross sectional widths of the n-channel periphery gates be greater thanor equal to the memory array n-channel gates, with the p-channelperipheral gates being wider than both. The respective gate linesinclude a gate oxide layer 28, a conductive polysilicon layer 30, anoverlying WSi_(x) layer 32, an overlying novellus oxide layer 34, and aSi₃ N₄ capping layer 36.

Referring to FIG. 2, a photoresist masking layer 38 is provided oversecond gate line 20, second peripheral PMOS substrate area 22, thirdgate line 24, and memory array NMOS substrate area 26. An n-type LDDimplant 42, preferably As, is then provided into the exposed firstperipheral NMOS substrate area 18 adjacent first gate line 16. Anexample and preferred average concentration of As for regions 42 is8×10¹⁸ ions/cm³. An example depth for the peak concentration is 400Angstroms.

A p-type halo ion implant is subsequently conducted into the exposedfirst peripheral NMOS substrate area 18 adjacent first gate line 16,thus producing p-type halo ion implant regions 44. The p-type halo ionimplant is conducted at a first energy level to provide a p-type firstimpurity concentration at a first depth within first peripheral NMOSsubstrate area 18. The depth is preferably conducted to be deeper thanthe maximum concentration depth of As LDD regions 42. An example andpreferred p-type implant material is boron. An example and preferredimplant dose is 7×10¹² ions/cm² -1.5×10¹³ ions/cm² to provide an exampleaverage dopant concentration of from 1×10¹⁶ ions/cm³ to 1×10¹⁸ ions/cm³,with about 1×10¹⁷ ions/cm³ being preferred. An example preferred implantenergy is from 60 KeV to 100 KeV (70 KeV preferred) to provide a peakconcentration implant depth of 2000 Angstroms. Most preferably, thep-type halo implant is conducted as a series of implants angled from 0°,with an angle of about 30° from vertical (i.e., 0° being an examplepreferred angle. For example, a series of for 0° angled implants at 70KeV at 90° wafer orientations using respective doses of 1.0×10¹²ions/cm² is a preferred implant sequence. Such provides an advantage ofdesirably driving a portion of the halo implant beneath the gate.

Referring to FIG. 3, masking layer 38 is removed and wafer fragment 10is subjected to oxidizing conditions to form oxidized sidewalls 46 aboutthe illustrated gate lines, and to form oxide 48 over exposed peripheralNMOS area 18, peripheral PMOS area 22, and memory array NMOS area 26.

Thereafter and in a common step, phosphorous is blanket ion implantedinto exposed first peripheral NMOS substrate area 18, second peripheralPMOS substrate area 22, and memory array NMOS substrate area 26 adjacentthe first, the second, and the third gate lines, respectively. Thisforms peripheral NMOS transistor LDD regions 50, peripheral PMOStransistor n-type halo regions 52, and memory array NMOS transistorsource/drain diffusion regions 54. The phosphorous implant is conductedat a second energy level to provide respective n-type second impurityconcentrations at a second depth within the first, the second and thememory array substrate areas. The first energy level and the first depthof implants 44 are chosen to be greater than the second energy level andthe second depth, respectively, of the blanket phosphorus implant. Mostpreferably, the implant energy difference between the p-type haloimplant and the n-type blanket implant is greater than or equal to 10KeV to provide the peak concentration of regions 44 at 1000 Angstromsbelow that of regions 50. An example energy level for the phosphorousimplant is from 30 Kev is to 60 KeV, with 30 KeV being preferred. Anexample and desired dose is from 7×10¹² ions/cm² -1.5×10¹³ ions/cm² toprovide an example average dopant concentration of diffusion regions 50,52 and 54 of from 1×10¹⁷ ions/cm³ to 1×10¹⁹ ions/cm³, with about 8×10¹⁷ions/cm³ being preferred.

The above described sequence is the preferred order by which therespective implants occur. The subject orders could be changed withoutdeparting from the principals and scope of the invention which isintended to be limited only by the accompanying claims appropriatelyinterpreted in accordance the Doctrine of Equivalents. Most preferably,the As LDD implant is conducted before the sidewall and substrateoxidations. The p-type halo implant is preferably conducted eitherbefore or after such oxidations. And, the greatest success was achievedwhere the blanket phosphorous implant is conducted after the sidewalland substrate oxidations.

Referring to FIG. 4, oxide or nitride sidewall spacers 60 are providedabout the illustrated respective gate lines. Thereafter, a photoresistmasking layer 62 is provided and patterned to expose peripheral NMOStransistor area 18 and mask the illustrated array and p-channelperiphery areas 22 and 26. An n-type implant is thereafter conducted toprovide n-type diffusion regions 64 for the peripheral NMOS transistorsto essentially complete formation thereof.

Referring to FIG. 5, the n-channel transistors are masked with aphotoresist layer 66, and ion implantation is conducted with a p-typematerial (i.e., boron) into the peripheral PMOS transistor to formdesired p-type source/drain diffusion regions 68.

Most preferably, additional doping in the memory array area relative tosource/drain diffusion regions 54 is not required or conducted.

P-type halo implant 44 is provided principally for improving/eliminatingshort channel effects in the peripheral n-channel transistors.Accordingly with respect to the above described preferred embodiment,the single masking step of FIG. 2 provides several advantageousfunctions. The initial, FIG. 2 doping enables provision of desiredp-type n-channel halo implants 44. The subsequent blanket phosphorousimplant provides the combination of a p-channel halo, a source/draindiffusion implant for the array, and reduction of n-channel peripheryLDD resistance which is much more desirable for the NMOS peripheraltransistors than for the NMOS array transistors. All FIG. 2 and 3implants are preferably conducted with the single FIG. 2 masking,whereas prior art methods use multiple masks to achieve the sameimplants.

The above described embodiment was described principally with referenceto formation of memory devices, such as DRAMs, that preferably utilizedtwo different types of NMOS transistors and one type of PMOStransistors. The artisan will as well appreciate that the invention hasapplication to non-memory devices including formation of three differenttransistor types. Further, the artisan will also appreciateapplicability of the invention to formation of CMOS circuitry onlyincorporating one type of NMOS transistor and one type of PMOStransistor.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A method of forming CMOS circuitry comprising:forming NMOS halo regions, NMOS LDD regions and NMOS source/drain regions; forming PMOS halo regions and PMOS source/drain regions; at least one maskless blanket doping step to form at least one of the NMOS regions and at least one of the PMOS regions; and no more than two masking layer provision steps to collectively form the NMOS halo regions, the NMOS LDD regions, the NMOS source/drain regions, the PMOS halo regions, and the PMOS source/drain regions.
 2. A method of forming CMOS circuitry comprising:forming NMOS halo regions, NMOS LDD regions and NMOS source/drain regions; forming PMOS halo regions and PMOS source/drain regions; forming memory array transistor source/drain regions; at least one maskless blanket doping step to form at least one of the NMOS regions, at least one of the PMOS regions, and the memory array source/drain regions; and no more than two masking layer provision steps to collectively form the NMOS halo regions, the NMOS LDD regions, the NMOS source/drain regions, the PMOS halo regions, the PMOS source/drain regions, and the memory array transistor source/drain regions.
 3. A method of forming CMOS circuitry comprising:forming NMOS halo regions, NMOS LDD regions and NMOS source/drain regions; forming PMOS halo regions and PMOS source/drain regions; at least one maskless blanket doping step to form at least one of the NMOS regions and at least one of the PMOS regions; and no more than three masking layer provision steps to collectively form the NMOS halo regions, the NMOS LDD regions, the NMOS source/drain regions, the PMOS halo regions, and the PMOS source/drain regions.
 4. A method of forming CMOS circuitry comprising:forming NMOS halo regions, NMOS LDD regions and NMOS source/drain regions; forming PMOS halo regions and PMOS source/drain regions; forming memory array transistor source/drain regions; at least one maskless blanket doping step to form at least one of the NMOS regions, at least one of the PMOS regions, and the memory array source/drain regions; and no more than two masking layer provision steps to collectively form the NMOS halo regions, the NMOS LDD regions, the NMOS source/drain regions, the PMOS halo regions, the PMOS source/drain regions, and the memory array transistor source/drain regions.
 5. A method of forming CMOS integrated circuitry on a substrate, comprising the steps of:providing said substrate having first and second portions; providing first and second gate areas on said substrate, the first gate area being positioned relative to the first portion of said substrate for formation of a first transistor, the second gate area being positioned relative to the second portion of said substrate for formation of a second transistor; forming a first transistor gate over the first gate area and a second transistor gate over the second gate area; masking said second transistor gate and said second portion of the substrate and conducting an implant of a second conductivity-type impurity into said first portion; removing said masking; after removing the masking, forming sidewall spacers adjacent the transistor gates; and after forming the sidewalls adjacent the transistor gates, implanting an impurity into said first and second substrate portions. 